1. Field of the Invention
The present invention relates to a current detecting device, a motor controlling system, an image forming apparatus, a sheet conveying device, a robot, and a current detecting method.
2. Description of the Related Art
Currently known image forming apparatuses employ brushless three-phase direct-current (DC) motors in paper conveying mechanisms or the like. A brushless three-phase DC motor operates with three phases, and therefore three current sensors corresponding to the respective phases are needed in principle in detecting current therethrough. It has been known that use of a current detection approach called the “single-shunt approach” enables current detection in the respective phases with one current sensor (a shunt resistor).
Japanese Unexamined Patent Application Publication No. 2011-147306 discloses a control circuit of an electric motor, the control circuit being configured to correct fluctuations in the value of the voltage across a shunt resistor that have been caused by the influence of the power supply voltage, thereby being capable of accurately detecting current that flows through the one shunt resistor.
However, the control circuit of an electric motor disclosed in Japanese Unexamined Patent Application Publication No. 2011-147306 needs a measurement circuit that directly detects the value of the power supply voltage. The control circuit thus has the disadvantages of having a complicated configuration and consequently being expensive to manufacture.